Vehicles designed for earthmoving applications are frequently equipped with earthmoving implements that are variably positonable. Motor graders, for example, may be equipped with blade control systems, such as a center shift mechanism, which enable the operator to select a wide variety of blade positions. The center shift mechanism is held in one of the variable preselected positions by a locking arrangement consisting of a lock pin and an actuating control circuit. Examples of such locking arrangements may be found in U.S. Pat. No. 3,692,149, issued Sept. 19, 1972 to J. H. Evans, in U.S. Pat. No. 3,739,861 which issued June 18, 1973 to H. M. Johnson et al., and in John Deere publication TM-1123 dated Feb. 1975.
However, such prior art locking arrangements are awkward and inefficient to use. The alignment of the variable position implement system is achieved by simultaneous manipulation of the system controls and visual observation of the members as they move from one preselected position to another. The lock pin cannot be engaged properly if these members are not aligned, and failure to completely engage the lock pin may result in damage to the vehicle or improper operation. A method of automatically engaging the lock pin with an indexing force upon alignment of the members is desired. However, the relatively great locking force is not suitable for this purpose, because as the lock pin slides across the face of the locking member, it would cause excessive wear or damage to the locking mechanism and to other members of the center shift mechanism. Additionally, the pin impinging on the locking member under the substantial locking force creates a braking force which acts on the center shift mechanism. This braking force in turn places a greater burden upon the vehicle power system and results in a reduction in efficiency.